The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks that generally sit in numerous distinctive layers. In order to understand this complex structure changes must be identified that distinguish one rock or mineral from another and to correlate them across wide lateral separation. Samples of layered rock are easily collected from vertical outcrops, either man-made (e.g., road cuts) or natural (e.g., mountainsides or valleys). When outcrops are not available or when the rocks are very deep, wells and cores provide access to samples of the rock not visible at the surface. Whether understanding the substrate for construction, environmental studies, water resources, mining, or oil and gas extraction, it is critical to recognize and understand the regional and local geology.
Numerous tools and techniques exist that provide information about rocks and minerals that might be encountered, ranging from direct chemical analysis to remote sensing of a multitude of physical rock parameters. Analyses of rock samples can be performed in an onsite or distant laboratory, or measurements can be taken remotely with tools lowered into holes or wells drilled into the rock or sediment. Some techniques are quite simple, and others are very expensive and complicated. For example, some tools and techniques measure different parameters, measure them using different methods or from different locations, analyze the measured data in different ways, and present the results of analysis in a variety of formats. Nevertheless, all of these tools and techniques work together to provide various properties and/or attributes of information that a trained person can use to identify, understand, and correlate specific rocks and minerals.
When describing a rock or mineral, not all of the information that a geologist might use is easily quantifiable. Geologic descriptions are commonly full of qualitative terminology and assessments. A geologist might use words such as “sandy,” “shaley,” “greenish,” “gray,” or “translucent” that may describe the grain size, texture, color, and so forth. The geologist might further qualify such descriptions with various modifiers—such as “light” or “dark,” to better describe the specific way a rock sample appears to an observer. Whereas the human eye is good at seeing fine details and discriminating subtle distinctions of texture and color, the human brain is not good at converting these fine distinctions into language that can be easily and clearly understood by another person with the same level of detail as the observer's eye. In addition, the brain cannot retain an image with enough detail to unequivocally determine if one sample is identical to another sample previously observed. Even the use of color charts similar to those used to match paint samples is limited in precision and repeatability. Geologists therefore, are not always able to easily and/or accurately quantify information observed during the study of rocks and mineralogy.